Ultrasound system for imaging and protecting ophthalmic or other sensitive tissues

ABSTRACT

An ultrasound imaging system includes a processor programmed to identify the type of tissue being imaged and to confirm that one or more system settings and/or the energy of ultrasound imaging signals delivered is set appropriately for such tissue. In one embodiment, an image obtained with the ultrasound imaging system is analyzed to determine if the tissue is ophthalmic (eye) tissue. If so, the system parameter settings and/or the transmit power of the signals produced by the ultrasound system are adjusted or maintained at a level that is appropriate for imaging such tissue.

TECHNICAL FIELD

The disclosed technology relates to ultrasound imaging systems and inparticular to ultrasound imaging systems that are useful in imagingophthalmic or other sensitive tissues.

BACKGROUND

Ultrasound is becoming an increasingly used, non-invasive imagingtechnique for examining ophthalmic (e.g. eye) tissue to asses tissuehealth, trauma or disease. With ultrasound imaging, high frequencyacoustic waves are transmitted into the tissue and the correspondingecho signals are detected and analyzed. One or more characteristics ofthe echo signals such as their amplitude, phase and frequency shift areanalyzed and represented in an image of the tissue.

One potential danger with ultrasound imaging is if the energy deliveredinto the tissue is great enough to cause heating of the tissue and/orcavitation in fluids. These effects are particularly dangerous whenultrasound signals are applied to the eye.

While most ultrasound operators are trained to apply a safe level ofultrasound energy to ophthalmic or other sensitive tissues, suchexaminations may be performed on the battlefield, at accident sites orin otherwise chaotic situations where mistakes can be made. In addition,human error may cause an operator to forget to set the transmit power ofan ultrasound imaging system to the appropriate level before examiningsensitive tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram of an ultrasound imaging system forobtaining and displaying images of ophthalmic tissue in accordance withone embodiment of the disclosed technology;

FIG. 2 is a block diagram of an ultrasound imaging system in accordancewith an embodiment of the disclosed technology;

FIG. 3 illustrates a typical ultrasound image of eye tissue; and

FIG. 4 illustrates measurements that can be obtained from an ultrasoundimage in order to determine whether the image represents ophthalmictissue.

DETAILED DESCRIPTION

As will be explained in further detail below, the disclosed technologyrelates to improvements in ultrasound imaging systems and in particularto an ultrasound imaging system that reduces the likelihood that excessacoustic energy will be delivered to sensitive tissues such asophthalmic tissue. In one embodiment, a processor is programmed toanalyze an ultrasound image to determine if the tissue being imaged islikely ophthalmic tissue. If so, the processor acts to produce an alertthat prompts an operator to confirm that the settings for the ultrasoundmachine are appropriate for this type of tissue and/or that the acousticenergy produced is within an acceptable range. In another embodiment,the processor is programmed to confirm that the settings are appropriateand/or that the acoustic energy of the signals produced is within a saferange for ophthalmic tissue before a scan begins. In one embodiment, theultrasound system obtains an image of the tissue and the processor isconfigured to analyze the image to determine if the tissue is notophthalmic or other sensitive tissue. If the tissue is not ophthalmictissue, then the system settings and/or acoustic energy produced can bechanged either under program control or by an operator. Otherembodiments are also disclosed.

FIG. 1 shows an exemplary ultrasound imaging system that implements thedisclosed technology for imaging an eye of a patient. In the embodimentdisclosed, an ultrasound imaging system 10 can be a hand held, portableor cart-based system that uses a transducer probe 12 to transmitultrasound signals into a region of interest and to receive thecorresponding echo signals in order to produce an image of the tissuebeing scanned. The probe 12 can include a single element transducer thatis mechanically moved to sweep the transducer over a range of beamangles. Alternatively, the probe 12 can include a one or two dimensionalphased array that can selectively change the transmit and receive beamangles electronically.

The ultrasound imaging system 10 operates to convert the received echosignals into an image that can be viewed by an operator, storedelectronically for digital record keeping or transmitted via a wired orwireless communication link to another device or location. In accordancewith some embodiments of the disclosed technology, the ultrasoundimaging system includes a processor that is programmed to determine ifthe tissue being imaged is likely ophthalmic tissue for which the energyof the ultrasound signals delivered should be selected to be in a rangethat is safe for such tissue.

In some embodiments, a processor in the ultrasound imaging system usesimage recognition technology to determine if an image produced by thesystem likely represents ophthalmic tissue. If so, the system settingsand/or transmit energy is checked to confirm they are safe for imagingsuch tissue. If the settings are wrong or the transmit energy is toohigh, the processor is programmed to change the settings or turn downthe transmit level or to alert the user to select an appropriate imagingstate that is safe for ophthalmic imaging. In an alternate embodiment,the system settings are set for sensitive tissues and/or the transmitenergy of the ultrasound system is limited until the processor candetermine that the tissue being imaged is not a sensitive tissue. Onceit is determined that the tissue is not ophthalmic or other sensitivetissue, the system settings and/or transmit energy level can beincreased either by the processor or by an operator.

In still other embodiments, the transducer probe can include a smallimaging camera similar to those found on cellular telephones. Imaginescaptured by the camera as the probe is being used, or is about to beused, are analyzed by the processor to determine the type of tissuebeing examined. If the images indicate that the tissue is ophthalmictissue, the processor in the ultrasound system can produce an alert orset the system settings and/or transmit energy of the ultrasound signalsdelivered to be within a safe range.

FIG. 2 shows a simplified block diagram of an ultrasound imaging systemin accordance with an embodiment of the disclosed technology. As will beappreciated by those skilled in the art, the ultrasound system may beconstructed with components that are different than those shown. Inaddition, the ultrasound system includes components that are notdiscussed (e.g. a power supply etc.) and that are not necessary for anunderstanding of how to make and use the disclosed technology. In theembodiment shown, the ultrasound system includes processor 40 having abuilt-in or external memory (not shown) containing instructions that areexecutable by the processor to operate the ultrasound imaging system aswill be explained in detail below. In the transmit path, the ultrasoundsystem includes a transmit beamformer 42, a transmit gain controlamplifier 44 and a transmit/receive switch 46. If the ultrasound probe12, is a phased array type, the transmit beamformer 42 operates togenerate a number of signals having a relative amplitude and phase(timing) selected to produce an ultrasound beam from the transducerelements of the probe that constructively adds in a desired direction(the desired beam angle). The signals from the transmit beamformer areamplified by the transmit amplifier 44 to a sufficiently high voltagelevel that will cause the transducer elements to produce the desiredacoustic signals in the tissue being examined.

In some embodiments, the processor 40 is connected to supply a controlcommand such as a digital value of 0-255 to the transmit gain controlamplifier to control the amount of energy in the signals produced. Themanner in which the energy of the ultrasound signals is varied caninclude controlling the voltage rails (+V, −V) on the transmit amplifier44 or changing one or more of the amplitude or duty cycle of the signalsproduced or supplying the signals to a varying number of transducerelements that transmit the signal pulses.

The amplified transmit signals are supplied to the transducer probe 12through the transmit/receive switch 46, which disconnects or shieldssensitive receive electronics from the transmit signals at the time theyare delivered to the transducer probe 12. After the signals aretransmitted, the transmit/receive switch 46 changes positions andconnects the receive electronics to the transducer elements to detectthe corresponding electronic echo signals created when the returningacoustic waves impinge upon the transducer elements.

In the receive path, the ultrasound imaging system includes a low noiseamplifier 50, a time gain control (TGC) amplifier 52, an analog todigital converter 54, a receive beamformer 56 and an image processor 58.Analog echo signals produced by the imaging probe are directed throughthe transmit/receive switch 46 to the low noise amplifier where they areamplified. The TGC amplifier 52 applies a variable amplification to thereceived signals according to the return time of the signals (e.g.proportional to the depth in the tissue being imaged to counteract theattenuation of the signals versus depth). The amplified signals are thenconverted into a digital format by the analog to digital converter 54.The digitized echo signals are then delayed and summed by the receivebeamformer 56 before being supplied to the image processor.

Images produced by the image processor 58 from the received signals aredisplayed on a display 60. In addition, the images can be recorded in animage memory (not shown) for future recall and review. A number ofinputs 72 are provided to allow an operator to change the operatingparameters of the ultrasound imaging system and to enter data such asthe patient name or other record keeping data. In addition, theultrasound imaging system includes input/output (I/O) circuitry to allowthe system to connect to computer communication links (LAN, WAN,Internet etc.) through a wired (e.g. Ethernet, USB, Thunderbolt,Firewire, or the like) or wireless (802.11, cellular, satellite,Bluetooth or the like) communication link. I/O circuitry can alsoinclude one or more speakers for communicating with a user.

The details of the components that comprise the ultrasound imagingsystem and how they operate are generally considered to be well known tothose of ordinary skill in the art. Although the ultrasound imagingsystem is shown having many separate components, it will be appreciatedthat devices such as ASICs or digital signal processors (DSPs) may beused to perform the function of multiple ones of these individualcomponents.

As discussed above, the processor 40 is programmed to lessen thelikelihood that high power ultrasound signals will be applied tosensitive tissues such as the eye. In one embodiment, when the tissuebeing examined is ophthalmic tissue, the processor is programmed togenerate an alert to the operator to check the system settings or tocontrol the energy delivered so that the tissue being examined isunlikely to be damaged by the ultrasound signals. Although the disclosedtechnology is described in the context of limiting the amount of energydelivered to ophthalmic tissues, the technology can also be used tolimit the amount of energy delivered to a fetus or other sensitivetissues.

In one embodiment, the processor 40 is programmed to analyze imagesproduced by the image processor 58 to determine if the image representsophthalmic tissue or other sensitive tissue for which the energydelivered to the tissue should be limited. In another embodiment, theprocessor analyzes images produced by the image processor 58 todetermine that the tissue being imaged is not ophthalmic tissue. Theprocessor initially sets the system settings and/or transmit power to beat a level for imaging sensitive tissues and once the processor hasdetermined that the tissue being imaged is not ophthalmic or othersensitive tissue, the processor or a user is allowed to change thesystem settings and/or increase the transmit power.

In some embodiments, the processor of the ultrasound system isprogrammed to estimate possible bio-effects of the ultrasound signalsdelivered to tissue using a certified model that relates the transmitvoltage to one or more imaging parameters such as mechanical index (MI),thermal index (TI), and spatial peak temporal average intensity (SPTA).To prevent damage to sensitive tissue, the processor uses the model todetermine the correct transmit voltage that will not exceed arecommended value for any of these parameters. To prevent damage tosensitive tissue, the processor detects that sensitive tissue is beingimaged and alerts the user to confirm that the parameter values are safefor such tissues. Alternatively, the processor selects the parametervalues that are safe for such tissues or can set the parameters to havevalues that are safe for such tissues until it is confirmed that suchsensitive tissues are not being imaged. In other embodiments, someimaging modes (e.g. color Doppler) that require higher energytransmissions than B-mode or M-mode imaging are not enabled until it isconfirmed such imaging modes are safe for the tissue type beingexamined.

FIG. 3 illustrates a typical ultrasound image of an eye. Variousanatomical features in the image can be seen as bright areas comparedwith the low intensity (e.g. black) regions from which little echosignal is received. Two features that are easily detectable in the imageare the rear surface of the lens and the retina. In most humans, theseshapes tend to be fairly regular and of a generally uniform size.Therefore, in one embodiment, the processor (or DSP or graphicsprocessor) is programmed to analyze an image produced by the graphicsprocessor to detect the presence or absence of one or more of thesefeatures. If one or more of these features is present, then theprocessor is programmed to classify the tissue as likely beingophthalmic. If these features are not present, then the processor canclassify the tissue as likely not being ophthalmic. In some embodiments,a full resolution image that is suitable for diagnostics is analyzed todetect the presence of sensitive tissues. In another embodiment, animage is produced with less resolution (e.g. from fewer scanlines) inorder to speed processing. In some embodiments, multiple images may beanalyzed and combined to detect the presence of sensitive tissue.

FIG. 4 shows one method of identifying ophthalmic tissue. In this case,the processor is programmed to analyze the brightness of the pixels thatcomprise the image to identify structures that may represent a lens anda retina. In some embodiments, the processor analyzes the pixelintensities and/or pixel gradients to locate bright pixels that arenearby corresponding dark pixels. The processor is programmed toidentify a set of pixel points (L) that may represent a lens and anadditional set of pixel points (R) that may represent a retina. On atwo-dimensional image, each pixel point has a corresponding X,Ycoordinate pair (or set of polar coordinates). In one embodiment, theprocessor is programmed to fit a curve to the sets of coordinates and toanalyze the curves to determine what anatomical object the curves likelyrepresent. In one embodiment, the processor is programmed to analyze thecurve representing the set of points L to determine for example, thedistance of the curve away from the transducer and its radius. If thesevalues fall within a range typically associated with a lens of an eye,then the computer can determine that the set of points likely representsa lens. In one embodiment, similar steps are performed on the set ofpoints R to determine if the set of points likely represents a retina.In some embodiments, other measurements such as one or more of thedistance D1 between the transducer and the set of points L, the distanceD2 between the transducer and the set of points R and the distance D3between the set of points L and the set of points R can be analyzed todetermine if these values fall within ranges typically associated withthe human eye.

Other techniques such as comparing a new ultrasound image produced bythe image processor 58 with one more ultrasound images stored in adatabase memory 70 that are known to represent eye scans can beperformed using for example, a sum of differences squared or other imagecomparison algorithms. Other algorithms as used in facial recognitionfor example, can be used to compare an image of the tissue with knownimages of ophthalmic tissues or other sensitive tissues (e.g. fetalimages). In the case of other sensitive tissues like fetal tissues, theprocessor 40 (or DSP or GPU) is programmed to analyze images for pixelsthat represent features commonly found in such tissues or to compareagainst fetal images using image comparison algorithms.

Once it is determined that the tissue that was imaged likely is or isnot ophthalmic tissue, the system settings can be changed or the energyof the acoustic signals that are produced by the transducer can beadjusted down if the energy is too high or up if it is safe to do so.

Although the above description is described with respect to humanophthalmic tissues, it will be appreciated that the eyes of animals(cats, dogs, horses etc.) are similar enough that the same type ofanalysis can be performed if the ultrasound imaging system is designedto be used in a veterinary setting. Similarly, other ultrasound imagescan be analyzed for the presence of other sensitive tissues, such asfetal tissue. Similarly, the ultrasound images can be analyzed by theprocessor to confirm the absence of such sensitive tissues beforeallowing the transmit power to be increased.

In some embodiments, if the processor detects the presence of suchtissue, the processor is programmed to trigger an alarm (e.g. visual onthe display screen 60, audible on a speaker that is part of the I/O 74or a tactile alarm such a vibration) to alert the operator to confirmthat the system settings are correct and/or that the power level isappropriate for the type of tissue being imaged. In other embodiments,the processor is programmed to change the system settings or reduce thetransmit power under program control. In still other embodiments, theprocessor is programmed to begin imaging with system settings that arecorrect for sensitive tissue at a power level that is safe for suchsensitive tissues and to prevent the power level from being increaseduntil such time as it is determined that such sensitive tissue is notbeing imaged.

In some embodiments, other mechanisms are used to identify the tissuebeing imaged. For example, the ultrasound transducer can be equippedwith a camera 80 (FIG. 2) similar to those commonly found on cellulartelephones or with an infrared camera. A camera control chip 82 iscontrolled by the processor to interact with the camera 80 and produceblack and white or color images. The output of the camera control chipcan be supplied to the image processor 58, to the processor 40 or can bestored in a memory. Images obtained with the camera can be analyzed withfeature or pattern recognition software algorithms to identify thetissue to be imaged with the ultrasound imaging machine. For example, ifthe camera obtains an image of tissue before the ultrasound signals areapplied, the processor may be programmed to analyze the image for thepresence of a circle of dark pixels (e.g. the pupil) surrounded bycolored pixels (the iris). If an image contains these features, theprocessor can adjust the system settings and/or the power of theacoustic signals produced by the transducer to be safe for ophthalmictissues.

The subject matter and the operations described in this specificationcan be implemented in digital electronic circuitry, or in computersoftware, firmware, or hardware, including the structures disclosed inthis specification and their structural equivalents, or in combinationsof one or more of them. Embodiments of the subject matter described inthis specification can be implemented as one or more computer programs,i.e., one or more modules of computer program instructions, encoded oncomputer storage medium for execution by, or to control the operationof, data processing apparatus.

A computer storage medium can be, or can be included in, acomputer-readable storage device, a computer-readable storage substrate,a random or serial access memory array or device, or a combination ofone or more of them. Moreover, while a computer storage medium is not apropagated signal, a computer storage medium can be a source ordestination of computer program instructions encoded in anartificially-generated propagated signal. The computer storage mediumalso can be, or can be included in, one or more separate physicalcomponents or media (e.g., multiple CDs, disks, or other storagedevices). The operations described in this specification can beimplemented as operations performed by a data processing apparatus ondata stored on one or more computer-readable storage devices or receivedfrom other sources.

The term “processor” encompasses all kinds of apparatus, devices, andmachines for processing data, including by way of example a programmableprocessor, a computer, a system on a chip, or multiple ones, orcombinations, of the foregoing. The apparatus can include specialpurpose logic circuitry, e.g., an FPGA (field programmable gate array)or an ASIC (application-specific integrated circuit). The apparatus alsocan include, in addition to hardware, code that creates an executionenvironment for the computer program in question, e.g., code thatconstitutes processor firmware, a protocol stack, a database managementsystem, an operating system, a cross-platform runtime environment, avirtual machine, or a combination of one or more of them. The apparatusand execution environment can realize various different computing modelinfrastructures, such as web services, distributed computing and gridcomputing infrastructures.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, declarative orprocedural languages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, object, orother unit suitable for use in a computing environment. A computerprogram may, but need not, correspond to a file in a file system. Aprogram can be stored in a portion of a file that holds other programsor data (e.g., one or more scripts stored in a markup languagedocument), in a single file dedicated to the program in question, or inmultiple coordinated files (e.g., files that store one or more modules,sub-programs, or portions of code). A computer program can be deployedto be executed on one computer or on multiple computers that are locatedat one site or distributed across multiple sites and interconnected by acommunication network.

The processes and logic flows described in this specification can beperformed by one or more programmable processors executing one or morecomputer programs to perform actions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application-specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read-only memory ora random access memory or both. The essential elements of a computer area processor for performing actions in accordance with instructions andone or more memory devices for storing instructions and data. Generally,a computer will also include, or be operatively coupled to receive datafrom or transfer data to, or both, one or more mass storage devices forstoring data, e.g., magnetic, magneto-optical disks, or optical disks.However, a computer need not have such devices. Devices suitable forstoring computer program instructions and data include all forms ofnon-volatile memory, media and memory devices, including by way ofexample semiconductor memory devices, e.g., EPROM, EEPROM, and flashmemory devices; magnetic disks, e.g., internal hard disks or removabledisks; magneto-optical disks; and CD-ROM and DVD-ROM disks. Theprocessor and the memory can be supplemented by, or incorporated in,special purpose logic circuitry.

From the foregoing, it will be appreciated that specific embodiments ofthe invention have been described herein for purposes of illustration,but that various modifications may be made without deviating from thescope of the invention. Accordingly, the invention is not limited exceptas by the appended claims.

I/We claim:
 1. An ultrasound imaging system comprising: an imageprocessor that is configured to produce an image of tissue beingexamined from received ultrasound signals; and a processor that isconfigured to analyze the image to determine if the tissue being imagedis sensitive tissue and if so, to confirm that the energy delivered bythe ultrasound imaging system is safe for imaging such sensitive tissue.2. The ultrasound imaging system of claim 1, wherein the sensitivetissue is ophthalmic tissue.
 3. The ultrasound imaging system of claim2, wherein the processor is configured to analyze the image of thetissue for the presence of anatomical structures present in an eye. 4.The ultrasound imaging system of claim 1, wherein the sensitive tissueis fetal tissue.
 5. The ultrasound imaging system of claim 1, whereinthe processor is configured to confirm that the energy delivered is safefor the sensitive tissue by producing an alert to a user to confirm thatone or more system settings are correct for imaging the sensitivetissue.
 6. The ultrasound imaging system of claim 1, wherein theprocessor is configured to begin imaging by producing ultrasound signalswith a transmit power level that is safe for sensitive tissues and toallow the transmit power level to be increased if the processordetermines that the tissue being imaged is not sensitive tissue.
 7. Theultrasound imaging system of claim 1, wherein the processor isconfigured to confirm that the energy delivered is safe for sensitivetissue by reducing the transmit power of ultrasound signals produced. 8.The ultrasound imaging system of claim 7, wherein the processor isconfigured to control the power level of the ultrasound signals producedby controlling a maximum transmit voltage of the ultrasound signals. 9.The ultrasound imaging system of claim 7, wherein the processor isconfigured to control the power level of the ultrasound signals producedby controlling a duty cycle of the ultrasound signals.
 10. Theultrasound imaging system of claim 7, wherein the processor isconfigured to control the power level of the ultrasound signals producedby controlling a number of transmit elements in a transducer thatproduce the ultrasound signals.
 11. The ultrasound imaging system ofclaim 2, wherein the processor is configured to compare the imageproduced by the image processor with one or more ultrasound images knownto represent ophthalmic tissue.
 12. The ultrasound imaging system ofclaim 2, wherein the processor is configured analyze the image producedby the image processor for a representation of one or more anatomicalfeatures known to be present in an eye.
 13. An ultrasound imaging systemcomprising: an image processor that is configured to produce an image oftissue being examined; and a processor that is configured to analyze animage of the tissue being examined to determine if the tissue beingimaged is sensitive tissue and if so, confirm that a level of energydelivered to the tissue by ultrasound signals produced by the ultrasoundimaging system is appropriate for imaging sensitive tissue.
 14. Theultrasound imaging system of claim 13, wherein the processor isconfigured to produce an alarm that requests that a user confirm thatone or more settings of the ultrasound system are appropriate forimaging sensitive tissues.
 15. The ultrasound imaging system of claim13, wherein the sensitive tissue is ophthalmic tissue.
 16. Theultrasound imaging system of claim 13, wherein the sensitive tissue isfetal tissue.
 17. The system of claim 13, wherein the processor isconfigured to analyze an image produced by a camera on an ultrasoundprobe.
 18. The system of claim 13, wherein the processor is configuredto analyze an image produced from echo signals received by an ultrasoundprobe.